We propose to study the mechanisms of potential generation in the photoreceptors and the distal interneurons of the invertebrate compound eye. In most of our studies we will be utilizing single-step mutants of Drosophila melanogaster which have been specifically isolated for the purpose of these studies. From comparative investigations of these mutants with wild type using a variety of analytical techniques, we hope to gain insight into the phototransduction process and the organization of the retinal circuitry.